This invention relates to a phosphor pattern, a process for preparing the same, an organic alkali developing solution for forming the same, an emulsion developing solution for forming the same and a back plate for plasma display using the same.
In the prior art, as one of flat plate displays, there has been known a plasma display panel (hereinafter referred to as a "PDP") which enables multicolor display by providing a phosphor which emits light by plasma discharge.
In such PDP, flat front plate and back plate comprising glass are arranged in parallel with each other and facing to each other, both of the plates are retained at a certain interval by a cell barrier provided therebetween, and PDP has a structure that discharge is effected in a space surrounded with the front plate, the back plate and the cell barrier.
In such a cell, a phosphor is coated for display, and by discharge, the phosphor emits light by UV ray generated from filler gas, and the light can be recognized by an observer.
In the prior art, as a method for forming the phosphor, a method of coating a slurry liquid or a paste in which phosphors of the respective colors are dispersed is coated by a printing method such as screen printing has been proposed and disclosed in Japanese Provisional Patent Publications No. 115027/1989, No. 124929/1989, No. 124930/1989 and No. 155142/1990.
However, the above-mentioned phosphor-dispersed slurry liquid is a liquid state so that dispersion failure is likely caused by sedimentation of phosphors, etc. Also, when a liquid state photosensitive resist is used as the slurry liquid, there is a defect of markedly lowering in preservation stability with the progress of dark reaction. Moreover, the printing method such as screen printing is inferior in formation precision so that there are problems that it is difficult to cope with enlargement of a screen of PDP in the future, and others.
The method of using a liquid state photosensitive resist is a method in which respective components constituting a photosensitive resin composition containing phosphors are dissolved or mixed in a solvent which is capable of dissolving or dispersing the phosphors to prepare a liquid in which the phosphors are uniformly dissolved or dispersed in the solvent, and the liquid is directly coated to the above-mentioned substrate for PDP, and dried to form a phosphor pattern.
As a method for providing phosphors, there has been proposed a method of using a photosensitive element (it is also referred to as "a photosensitive film") containing phosphors (Japanese Provisional Patent Publications No. 267421/1994 and No. 273925/1994).
In the method of using a photosensitive film, a phosphor-containing photosensitive resin layer of a photosensitive film comprising a photosensitive resin layer containing a phosphor and a support film is embedded in the above PDP cell by contact bonding (lamination) under heating, the layer is subjected to imagewise exposure with active light such as UV ray by a photographic method using a negative film, an unexposed portion is removed by a developing solution such as an alkaline aqueous solution, and further unnecessary organic components are removed by calcination to form a phosphor only at a necessary portion.
When the above-mentioned photosensitive element is used, it is not necessary to confirm dispersibility of phosphors as conducted in a phosphor-dispersed slurry liquid or a phosphor-dispersed paste, and is excellent in preservation stability as compared with the phosphor-dispersed slurry liquid or the phosphor-dispersed paste. Moreover, since a photographic method is used, a phosphor pattern can be formed with good precision.
However, when a phosphor pattern is formed by directly coating a phosphor-containing liquid-state photosensitive resist to the above-mentioned substrate for PDP, or laminating on a substrate for the above-mentioned PDP a phosphor-containing photosensitive resin layer using a photosensitive element, then, image wisely exposing with an active light such as an ultraviolet ray, etc., according to the photographic method, thereafter removing an unexposed portion by a developing solution such as an alkaline aqueous solution, and further a phosphor pattern is formed by removing the organic component by calcination, there sometimes causes problems of changes in emission characteristics (such as emission luminance and chroma) of phosphors.